Nanoindentation was used to study incipient plastic deformation in the vicinity of grain boundaries of different character in Fe-3 mass% Si alloy bicrystals and tricrystal. Pop-in events associated with the grain boundaries were observed in the load-displacement curves. From the pop-in hardness values, the critical stresses required to propagate the yield past the grain boundary were estimated to be in the range of approximately A mu/400-A mu/130 (where A mu is the shear modulus) depending on the grain boundary character: the special boundaries usually had higher critical stresses than the general boundaries. A Hall-Petch (H-P) type relationship was found between the hardness and the distance of the indenter to the grain boundary. The H-P slopes obtained were approximately one order of magnitude lower than the macroscopic value of the H-P slope for the Fe-3 mass% Si alloy, and were generally lower for general grain boundaries than for special boundaries.